This invention relates to internal combustion engine ignition systems and, more particularly, to a solid-state ignition system.
Internal combustion engines which are to be used in "tomorrows" automobiles may be required to operate for an equivalent of 50,000 miles without any significant increase in pollutant emission. It has been recognized that present mechanical ignition systems are inadequate with respect to this requirement and that electronic ignition systems which are completely solid-state are needed. Several forms of solid-state ignition systems have been constructed to replace the conventional mechanical breaker point type of ignition systems now being used. These prior art solid-state ignition systems are mostly concerned with providing adequate sparking potential to operate the internal combustion engine and limiting the energization current produced thereby in order to protect transistorized output stages and the ignition coil.
Furthermore, because many automobiles today employ catalytic converters for reducing pollution emissions, it is important that sufficient spark potential be developed to prevent a no-spark condition from occurring during operation of the engine. If during either constant engine RPM operation or during engine acceleration, a spark does not occur in timed relationship to the engine cycle, raw fuel could be drawn directly into the catalytic converter. Since catalytic converters have high internal temperatures, the raw fuel could be ignited therein which might damage the converter. Therefore, it is of major concern that solid state ignition systems provide sufficient energization current to the primary winding of the ignition coil in correct timed relationship to the operation of the engine to ensure that a spark will be produced to prevent damage to the catalytic converter.
Thus a need exists for a solid-state ignition system which provides a fixed current-limit duty cycle of the energizing current with respect to the total time period of the firing cycle of the internal combustion engine.